Drifting fish aggregation devices (FAD) are used widely to aggregate and catch tropical tunas in the purse seine fishery. Dolphinfish (Coryphaena hippurus) is one of the common by-catch species in purse seine fishing with FADs. The study of their biological characteristics is helpful to better understand the population structure, and has important significance on the reasonable resource conservation. The biological characteristics (length distribution, sex ratio, sexual maturity and diet) of 189 individuals are analyzed using the fishery biological data collected by the scientific observers onboard purse seine fishing vessels operating in the Western and Central Pacific Ocean (5°N-10°S, 145°E-170°E) from 2010 to 2013. The results indicated (1) fork length of dolphinfish associated with drifting FADs ranged from 10.0 to 126.3 cm, with the dominant fork length of 70.0 to 100.0 cm, accounting for 66.7% of the total; (2) sex ratio is about 4.1:1, and a significant deviation (χ² =68.17, P<0.05) from the expected 1：1 female to male can be observed; (3) the mature individuals (Ⅴ-Ⅵ) were dominant under the FADs, accounted for 73.6%, and the estimated size at 50% maturity is 49.95 cm; (4) 76.0% of stomachs are empty, but some commonly small associated fish species, such as Katsuwonus pelamis, Decapterus macarellus, Caranx sexfasciatus, Canthidermis maculate, and Aluterus monoceros are found in the stomach of dolphinfish. The information of fishery biology suggests the mature and large individuals are dominant in the dolphinfish school associated with drifting FADs, which have a stronger aggregation effect on females, and feeding is one of the possible potential motivations for dolphinfish aggregating around the FADs.